Easiest way to make a copy of a record is to use "Duplicate Record / Request".
But this will duplicate the record after the data has changed giving you two copies of the new data. I think you'll want to duplicate the record befor using the user's input to modify a field in the record.
You may want to pop up a custom dialog or new window to display the data from the field in a global field for user edits and then if the new value is different from the original, duplicate the record and then use set field to update the modified field in one of two resulting copies of this record by copying the data from the global field to the original filed.
Another option may be to copy the data to a variable, revert the record, duplicate it and then copy from the variable back to the field.